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At least 91 records · Page 5Linked to original sources
PubMed1995

In-line microwave blood warming of in-date human packed red blood cells.

OBJECTIVE: To verify two hypotheses: a) In-line microwave warming of cold in-date packed red blood cells (RBCs) does not produce significant hemolysis; and b) in-line microwave warming achieves higher outlet temperatures as compared with current blood warming technology at high flow rates (> 250 mL/min). DESIGN: Multiple part, randomized, controlled study. SETTING: Surgical research laboratory of a large university medical center. SUBJECTS: Twenty-four units of cold, ready for transfusion in-date packed RBCs ranging in storage age from 6 to 16 days. INTERVENTIONS: Part I: Microwave apparatus outlet, warmed vs. unwarmed. Six units of cold packed RBCs was split into paired samples and infused at 13 mL/min through a 700-watt in-line microwave test apparatus. One paired specimen was warmed to 37 degrees C; the other was infused without warming (control). Blood was analyzed at the outlet. Part II: Microwave and countercurrent warming, inlet vs. outlet. Twelve units of cold packed RBCs was analyzed biochemically both before (inlet) and after (outlet) simulated transfusions. Six units was infused through a 900-watt in-line microwave test apparatus at > 500 mL/min. Six separate cold units were warmed at this rate using single channel countercurrent water bath warming. Part III: Microwave and countercurrent technology, inlet vs. outlet, warmed vs. unwarmed. a) Six units of cold packed RBCs was also analyzed biochemically and infused at 5 mL/min through either a microwave or countercurrent water bath warmer. b) Packed RBCs from the units used in part a) were allowed to remain stationary in the microwave heating cartridge for 15 mins with an activated heating element. Parallel stationary flow studies were done using the countercurrent blood warmer. Control unwarmed samples were also tested. MEASUREMENTS AND MAIN RESULTS: Part I: No statistical differences in hemolysis parameters were observed between microwave warmed and unwarmed packed RBCs. Part II: At high-flow rates, no statistical increases in hemolysis parameters were seen after in-line microwave or countercurrent water bath warming as compared with prewarmed cold controls. Part III: At slow-flow rates, nonstatistically significant increases were seen by passing the packed RBCs through either test apparatus unwarmed. Packed RBCs remaining stationary within microwave and countercurrent heating cartridges for 15 mins did show biochemical evidence of hemolysis. Mean plasma hemoglobin increased from 14 +/- 1.7 mg/dL in cold prewarmed units to 57.7 +/- 5.8 mg/dL (p < .05), when warmed in the microwave heating cartridge, and to 55.2 +/- 25 mg/dL (p < .05), when warmed in the countercurrent heat exchanger. Outlet Temperature Studies. Part II: The in-line 900-watt microwave device warmed cold units from a mean inlet temperature of 8.3 +/- 0.3 degrees C to a mean outlet temperature of 31.8 +/- 0.5 degrees C within 5 secs at a mean flow rate of 556 mL/min. At 30 secs, the mean outlet temperature was 33.9 +/- 0.4 degrees C (mean inlet temperature = 9.6 +/- 0.2 degrees C) for microwave warmed packed RBCs as compared with 32.1 +/- 0.5 degrees C (mean inlet temperature = 9.6 +/- 0.3 degrees C) in countercurrent water bath warmed blood (p < .05). From 20 to 30 secs, the packed RBCs warmed by microwave were statistically warmer than the countercurrent water bath warmed packed RBCs. CONCLUSIONS: a) Both in-line countercurrent warming and in-line microwave warming were associated with small increases in parameters of red cell damage representing statistically and clinically insignificant hemolysis. b) Blood sitting in any blood warming device is subject to statistically significant but clinically irrelevant increases in those parameters. c) At high-flow rates, the in-line microwave device warmed blood to higher outlet temperatures than the single channel countercurrent water bath warmer. This method may represent a clinical blood warming modality of the near future.

Blood Preservation↗
PubMed1998

Calibration and standardization of microwave ovens for fixation of brain and peripheral nerve tissue.

Rapid and reproducible fixation of brain and peripheral nerve tissue for light and electron microscopy studies can be done in a microwave oven. In this review we report a standardized nomenclature for diverse fixation techniques that use microwave heating: (1) microwave stabilization, (2) fast and ultrafast primary microwave-chemical fixation, (3) microwave irradiation followed by chemical fixation, (4) primary chemical fixation followed by microwave irradiation, and (5) microwave fixation used in various combinations with freeze fixation. All of these methods are well suited to fix brain tissue for light microscopy. Fast primary microwave-chemical fixation is best for immunoelectron microscopy studies. We also review how the physical characteristics of the microwave frequency and the dimensions of microwave oven cavities can compromise microwave fixation results. A microwave oven can be calibrated for fixation when the following parameters are standardized: irradiation time; water load volume, initial temperature, and placement within the oven; fixative composition, volume, and initial temperature; and specimen container shape and placement within the oven. Using two recently developed calibration tools, the neon bulb array and the agar-saline-Giemsa tissue phantom, we report a simple calibration protocol that identifies regions within a microwave oven for uniform microwave fixation.

Animals↗
PubMed1998

A high-efficiency microwave thermoablation system for the treatment of benign prostatic hyperplasia: results of a randomized, sham-controlled, prospective, double-blind, multicenter clinical trial.

OBJECTIVES: To determine the effectiveness, safety, and impact on patient quality of life (QOL) of a novel transurethral microwave thermoablation system for the treatment of benign prostatic hyperplasia (BPH). METHODS: A total of 169 patients with BPH were randomized to undergo a 1-hour microwave (n = 125) or sham (n = 44) procedure using the Urologix Targis thermoablation system on an outpatient basis, without general or regional anesthesia. Symptoms, flow rates, and QOL scores were determined before the study procedure and periodically thereafter up to 6 months. RESULTS: Mean American Urological Association (AUA) score in the microwave group diminished 50% (P <0.0005) by the 6-month evaluation (10.5, 95% confidence interval [CI] 9.2 to 11.8) compared with baseline values (20.8, 95% CI 19.8 to 21.9). The sham group also exhibited lower postprocedural AUA scores; however, the magnitude of the postprocedural decline in AUA score in the microwave group was significantly greater (P <0.01) than that in the sham group. Half the microwave group had an AUA score of less than 9 by 6 months, and the decrease in symptoms was similar among patients with initially moderate versus initially severe symptoms. Mean peak urinary flow rate (Qmax) in the microwave group increased 51% (P <0.0005) by 6 months to 11.8 mL/s (95% CI 10.7 to 13.0) versus a pretreatment value of 7.8 mL/s (95% CI 7.4 to 8.2). The magnitude of the postprocedural increase in Qmax was significantly greater in the microwave than the sham group (P <0.05). In nearly half the microwave group (47%), Qmax increased 50% or more by 6 months compared with 24% of the sham group. Microwave treatment resulted in a significantly greater (P <0.05) positive impact on patient QOL than did the sham procedure. By 6 months, the QOL score in microwave-treated patients (2.2, 95% CI 1.9 to 2.4) averaged 48% lower (P <0.0005) than that at baseline (4.2, 95% CI 4.0 to 4.4). Significantly greater durability of treatment effects was also evident with microwave than with sham treatment, as judged by the higher proportion of microwave-treated patients (98.4%) requiring no further treatment during the 6-month study period versus 83.3% of sham control patients (P <0.0005). Microwave treatment was well tolerated, and complications were generally minor, readily manageable, and transitory. CONCLUSIONS: The microwave thermoablation system proved to be an effective and safe treatment modality for BPH, with a positive impact on patient QOL.

Aged↗
PubMed1989

Effects of microwave radiation on the eye: the occupational health perspective.

The purpose of this overview is to promote an interest in understanding and reducing the possible occupational health risks of microwave radiation on the eye. Microwaves act on living tissue through two types of mechanisms, thermal and nonthermal. Lens opacities can be induced in experimental animals at relatively high intensities (power densities greater than 100 mW/cm2). For lower intensities, lens changes may depend on the cumulative dose. At "nonthermal intensities", microwaves can act as a trigger and set off changes in the living tissues (e.g. Ca++ efflux). Some cataract-causing agents (alloxan and galactose) act synergistically with microwaves. Microwaves also accelerate formation of cataracts due to diabetes. The corneal endothelium can be damaged by microwaves alone or in combination with some drugs. Microwave degeneration of retinal nerve endings and a small increase in retinal permeability were also found in animals. The effect of long-term low-intensity microwave exposure on the human lens remains poorly understood. Several reports have implicated occupational microwave exposure as a factor in increasing the rate of lens aging and retinal injury in microwave workers. In Canada, recommended microwave exposure limits are set at 25 mW/cm2 for microwave workers and at 1 mW/cm2 for the general public (both averaged over 1 minute). The Australian microwave exposure safety standard (1985) recommends pre- and post-employment eye examinations for workers.

Animals↗
PubMed1980

Alterations in activity at auditory nuclei of the rat induced by exposure to microwave radiation: autoradiographic evidence using [14C]2-deoxy-D-glucose.

Autoradiographic maps of brain activity in rats exposed to pulsed or continuous-wave (CW) microwave radiation were made using [14C]2-deoxy-D-glucose ([14C]2-DG). Special emphasis was given to measurements of activity in the auditory system because previous work had shown that pulsed microwave radiation can elicit auditory responses in man and other animals. In particular, one middle ear was ablated in nine rats to attenuate the transmission of air-borne sound to one cochlea. The resulting imbalance in auditory input for four animals not exposed to microwave radiation was reflected as a bilateral asymmetry of [14C]2-DG uptake at the inferior colliculus and medial geniculate body. In contrast, a symmetrical pattern of uptake at these structures in an animal exposed to pulsed microwave radiation showed that this stimulus bypasses the middle ear in eliciting auditory responses. This result established the utility of the [14C]2-DG method for demonstrating a known effect of microwave radiation on brain activity. The results also revealed responses at auditory nuclei in 4 animals exposed to CW microwave radiation. These responses, which have not been observed with other methods, were evident at the power densities of 2.5 and 10 mW/sq. cm. To exclude the possibility that CW microwave radiation produced this result by direct action on brain tissue, additional data were obtained from two rats with one cochlea destroyed. In both animals, the uptake of [14C]2-DG at the inferior colliculus and medial geniculate body was virtually identical to the uptake in animals not exposed to microwave radiation, i.e. greatest on the side of the brain contralateral to the intact cochlea. This finding, coupled with the finding of a bilateral symmetry of [14C]2-DG uptake in the auditory pathways of animals with one middle ear ablated, confirmed the hypothesis that auditory responses to CW microwave radiation originate within the cochlea. Effects on brain activity outside of the auditory system were not found in qualitative analyses of autoradiographs for the conditions of exposure to CW microwave radiation noted above or for exposure to pulsed microwave radiation at the average power density of 2.5 mW/sq. cm.

Animals↗
PubMed2004

Interaction of microwaves and a temporally incoherent magnetic field on spatial learning in the rat.

The effect of a temporally incoherent magnetic field ('noise') on microwave-induced spatial learning deficit in the rat was investigated. Rats were trained in six sessions to locate a submerged platform in a circular water maze. Four treatment groups of rats were studied: microwave-exposure (2450-MHz continuous-wave microwaves, power density 2 mW/cm(2), average whole-body specific absorption rate 1.2 W/kg), 'noise' exposure (60 mG), 'microwave+noise' exposure, and sham exposure. Animals were exposed to these conditions for 1 h immediately before each training session. One hour after the last training session, animals were tested in a 2-min probe trial in the maze during which the platform was removed. The time spent during the 2 min in the quadrant of the maze in which the platform had been located was scored. Results show that microwave-exposed rats had significant deficit in learning to locate the submerged platform when compared with the performance of the sham-exposed animals. Exposure to 'noise' alone did not significantly affect the performance of the animals (i.e., it was similar to that of the sham-exposed rats). However, simultaneous exposure to 'noise' significantly attenuated the microwave-induced spatial learning deficit (i.e. 'microwave+noise'-exposed rats learned significantly better than the microwave-exposed rats). During the probe trial, microwave-exposed animals spent significantly less time in the quadrant where the platform was located. However, response of the 'microwave+noise'-exposed animals was similar to that of the sham-exposed animals during the probe trial. Thus, simultaneous exposure to a temporally incoherent magnetic field blocks microwave-induced spatial learning and memory deficits in the rat.

Analysis of Variance↗